As shown in FIG. 1, pipes 100 are often warehoused in tiered racks 110. Three tiers are shown in FIG. 1, but pipe racks having five or more tiers are common in practice. Typically, the warehouse will have an overhead crane for moving the pipes. However, wrapping a crane sling around a pipe 100 disposed in a rack 110 is difficult, especially if the pipe 100 is not located on the top tier. Therefore, it is necessary to partially withdraw the pipe 100 from the rack 110 before the crane sling is wrapped around it. Prior methods of accomplishing this task were dangerous and often resulted in damage to an end of the pipe 100.
The present invention eliminates these drawbacks by providing a controllable means for withdrawing the pipe and reducing the possibility of damage to the pipe. The present invention also provides a useful means for inserting a pipe into a rack with minimal risk of damaging the pipe. A number of prior inventions disclose mechanisms for gripping and manipulating tubular structures, but none will perform satisfactorily when used to rack or unrack pipe.
Cullen et al. (U.S. Pat. No. 4,687,244) describe a lifting and reorienting mechanism. The device includes a probe for insertion into an axially extending opening of a structure to be moved. When fully inserted, movement of an outer sleeve deploys tooth-like retractable projections that extend radially from the probe. The retractable projections are forced against the inner wall of the structure to be moved. An important feature of the Cullen et al. device is a dual-arm telescoping actuator that facilitates pivoting of the probe and the structure to be moved. Although this device is capable of performing many useful functions, it is not well suited for the racking and unracking of pipes. The pivoting capability of the device is not required for pipe racking and unracking and might pose a safety hazard should it be accidentally activated. In addition, the retractable projections of the device are likely to damage the inner surface of the pipe.
Marzoli (U.S. Pat. No. 4,777,792) discloses a tube gripping device that is designed to be used in textile machines to automatically replace with empty tubes those tubes that have been wrapped with yarn. The gripping device comprises a substantially cylindrical central steel element that has its lower end of frusto-conical shape and is free to slide axially in a cylindrical gripping element. The cylindrical gripping element has its bottom shaped to receive the lower end of the cylindrical steel element. An axial upward movement of the cylindrical central element forces a localized region of the cylindrical gripping element radially outward, thereby pressing that region of the cylindrical gripping element against the inner wall of the tube. The radially outward movement of the cylindrical gripping element is localized in the vicinity of the frusto-conical lower end of the cylindrical central element. In addition, the radial motion is a direct response to the radial component of the force exerted on the cylindrical gripping element by the frusto-conical lower end of the cylindrical central element. The localized nature of the gripping force is not desirable for the pipe racking and unracking application being considered herein.
Mistrater et al. (U.S. Pat. No. 5,322,300) describe several variants of a device for supporting hollow cylinders while they are coated with an electrophotographic-imaging layer. The devices comprise an elongated arm with a shaft extending therethrough. The shaft includes a presser means at one end. An expandable disk shaped member is coaxially aligned with and slidably mounted on the shaft between the presser means and an end of the elongated arm. In an undeformed state, the expandable disk shaped member fits in a hollow cylinder with a preferred clearance of about 250 micrometers (0.01 in). Expansion of the disk shaped member is achieved by compressing the member between the presser means and the end of the elongated arm. Additional features of the Mistrater et al. device ensure that a constant force is applied to the hollow cylinder in spite of temperature variations. However, the Mistrater et al. device fails to provide a means for self-orienting the device coaxially with the hollow cylinder.